TISSUE DISTRIBUTION AND QUANTITATIVE-ANALYSIS OF ESTROGEN RECEPTOR-ALPHA (ER-ALPHA) AND ESTROGEN RECEPTOR-BETA (ER-BETA) MESSENGER-RIBONUCLEIC-ACID IN THE WILD-TYPE AND ER-ALPHA-KNOCKOUT MOUSE

Until recently, only a single type of estrogen receptor (ER) was thoug ht to exist and mediate the genomic effects of the hormone 17 beta-est radiol in mammalian tissues. However, the cloning of a gene encoding a second type of ER, termed ERP, from the mouse, rat, and human has pro mpted a reevaluation of the estrogen signaling system. Based on in vit ro studies, the ERP protein binds estradiol with an affinity similar t o that of the classical ER (now referred to as ER alpha) and is able t o mediate the effects of estradiol in transfected mammalian cell lines . Essential to further investigations of the possible physiological ro les of ERP, and its possible interactions with ER alpha, are data on t he tissue distribution of the two ER types. Herein, we have described the optimization and use of an RNase protection assay able to detect a nd distinguish messenger RNA (mRNA) transcripts from both the ER alpha and ER beta genes in the mouse. Because this assay is directly quanti tative, a comparison of the levels of expression within various tissue s was possible. In addition, the effect of disruption of the ER alpha gene on the expression of the ERP gene was also investigated using the ER alpha-knockout (ERKO) mouse. Transcripts encoding ER alpha were de tected in all the wild-type tissues assayed from both sexes. In the fe male reproductive tract, the highest expression of ER beta mRNA was ob served in the ovary and showed great variation among individual animal s; detectable levels were observed in the uterus and oviduct, whereas mammary tissue was negative. In the male reproductive tract, significa nt expression of ERP was seen in the prostate and epididymis, whereas the testes were negative. In other tissues of both sexes, the hypothal amus and lung were clearly positive for both ER alpha and ER beta mRNA . The ERKO mice demonstrated slightly reduced levels of ER beta mRNA i n the ovary, prostate, and epididymis. These data, in combination with the several described phenotypes in both sexes of the ERKO mouse, sug gest that the biological functions of the ER beta protein may be depen dent on the presence of ER alpha in certain cell types and tissues. Fu rther characterization of the physiological phenotypes in the ERKO mic e may elucidate possible ER beta specific actions.